Functionally Crosslinked Dense Film and Asymmetric Hollow Fiber Membranes for Simultaneous H2S and CO2 Removal From Sour Gas

A new class of crosslinkable membrane materials that are capable of simultaneously removing H₂S and CO₂ from sour gas feeds has been developed based on a glassy polyimide, 6FDA-DAM:DABA. Earlier variants involving propanediol crosslinked 6FDA-DAM:DABA have been improved upon by using alternative crosslinkers designed to augment the H₂S/CH₄ selectivity of these materials. Dense film permeation using a ternary mixture of 20% H₂S, 20% CO₂, and 60% CH₄ was conducted on a series of these crosslinkable materials at 35°C and at feed pressures up to 900psi. The H₂S/CH₄ selectivity increases by nearly a factor of three compared to the ideal H₂S/CH₄ selectivity of an uncrosslinked 6FDA-DAM:DABA membrane, going from a value of 8.3 to 23.7 in the crosslinked membrane. Also, the CO₂/CH₄ selectivity of these materials is actually enhanced to values greater than 40 in the presence of low partial pressure H₂S, and only a slight decrease from the ideal CO₂/CH₄ selectivity of these materials occurs at the highest acid gas partial pressures tested. The excellent separation efficiency, productivity, and plasticization resistance to both H₂S and CO₂ far exceed that of the limited number of other glassy materials that have been used for this application, including cellulose acetate. Based on a combined acid gas separation efficiency metric, these novel materials are competitive with even the highest performing rubbery polymer membranes, and are preferable based on a number of practical considerations. Initial dense film work, which involved material characterization and optimization of the crosslinking protocol, has led to current efforts to develop and crosslink asymmetric hollow fiber membranes.